This invention relates to internal combustion engines, and more particularly to variable displacement internal combustion engines.
As is known in the art, in order to reduce fuel consumption in a multi-cylinder internal combustion engine, it has been suggested to operate such engine during periods of low torque demand with only a portion of the cylinders. Such engines are sometimes referred to as variable displacement engines (VDEs). Thus, when the operator is not demanding engine torque, less than all cylinders are operational; however, when the operator demands a large amount of torque all cylinders are made operational. One problem with such system is that the transition between all cylinder operation and less than all cylinder operation may cause an unpleasant abruptness in the operation of the engine.
In accordance with the present invention, an engine is provided having a plurality of cylinder banks, each one of the banks having at least one cylinder. Each one of the banks is fed air through a corresponding one of a pair of manifold plenums. A main throttle body is provided having an outlet for feeding air to a pair of output ports, each one of such output ports being coupled to feed the air to a corresponding one of the pair of manifold plenums. The main throttle body has a main throttle plate disposed therein to control airflow passing to the outlet of the main throttle body. One of the pair of plenums has a plenum throttle plate for controlling air from the one of the pair of output ports of the main throttle body coupled thereto to cylinders in the bank of cylinders coupled thereto.
With such an arrangement, during transitions from an engine operation mode using a first number of the cylinders to a mode using a different number of the cylinders, the plenum throttle plate is operated to provide a change in airflow to said one of the pair of plenums in a first sense thereby changing the airflow in the other one of the bank of cylinders in a second, opposite sense.
Because, for any main throttle plate position, the mass airflow to the outlet of the main throttle body changes during the transition between engine operating modes as a result of different vacuum effects being produced by operating the engine with a different number of cylinders, airflow compensation is provided to maintain the airflow to the outlet of the main throttle body constant during the mode transition if the main throttle plate is held unchanged by an operator. In one embodiment, the airflow compensation includes providing a compensation control signal to the main throttle plate, as when an electronic throttle is used. In another embodiment, an airflow by-pass structure is coupled to the main throttle body upstream of the main throttle to adjust airflow downstream of the main throttle as the number of operating cylinders in the engine changes. With either embodiment, during the mode change, a substantially continuous total mass airflow is maintained to the operational cylinders and therefore a continuous and smooth change in engine torque output is achieved. Thus, the method produces a torque output which is similar to the torque output, which would be produced with a non-variable displacement engine (VDE).
In one embodiment, immediately before disabling or enabling cylinders in the one of the banks, the inlet airflow to such bank is kept to a minimum for minimum torque output while preventing such disabled or enabled cylinders from misfiring.
With such method, smooth engine torque changes are accomplished as the number of operating cylinder changes while the method maintains exhaust emissions requirements and good fuel economy.